The production of polymers based on acrylic monomers and styrene monomers is well known in the art. U.S. Pat. No. 3,983,268, for example, teaches the production of such polymers from, for example, methacrylic acid and styrene to produce highly random copolymers which are water-soluble. The process comprises slowly adding the styrene monomer to the entire concentration of the methacrylic acid monomer over the course of the reaction. The resultant polymers are neutralized with a base such as a caustic alkali and used with such materials as urea, dimethyl acetamide etc. as sizing agents for paper. U.S. Pat. No. 4,481,244 likewise teaches the production of polymers from such as monomers as styrene, acrylic acid and butyl acrylate using an isopropanol/water mixture as a solvent for the monomers and ammonium persulfate as the catalyst via an emulsion polymerization process. The monomers are added drop-wise over the course of the polymerization. Likewise, U.S. Pat. No. 4,628,071 teaches an emulsion polymerization process for the production of such polymers wherein a chain transfer agent is employed as is a gradual addition of monomers over the course of the polymerization.
The '071 process is complex to carry out. Furthermore, the immediate product is not an effective size per se and must be neutralized by a further complex series of steps. When completed, the final product has been found to possess unacceptable sizing properties due possibly to: a) its composition or b) to the difficulty of removing the original surfactants (which form the emulsion and are detriments to effective sizing) from the end product.
While it is the intent of all of these processes to produce a polymer having a substantially random configuration, because of the widely divergent reactivity ratios of the monomers, especially styrene and methacrylic acid, the methacrylic acid always tends to polymerize more rapidly and the styrene less rapidly, thus resulting in polymers wherein the initial sections of polymer are rich in methacrylic acid and the latter sections of polymer are rich in styrene. Attempts to get the monomers to react equally whereby the content of each in any particular section of the polymer chain will be substantially the same have proven less than successful.
Accordingly, the search for a process for the production of highly random polymers from these monomers continues and the discovery of such would fill a long-felt need in the industry.